The director once again let the info be known through his Twitter, and once again it's up to all of us to play the guessing game.
As there is an element of time travel to X-Men: Days of Future Past it's thought that Omar Sy might be portraying the mutant from the future with Bishop.
Of course, there are other contenders and one could be Forge.
I'll throw one out there for fun -- Deathlok?
There was a Deathlok from an alternate future that was featured in Rick Remender's recent run of Uncanny X-Force.
I think the "Days of Future Past" comic book story was only like two issues, so there is a lot Singer could do and go with.
Omar Sy is a French actor known for the Intouchables and Micmacs.
X-Men: Days of Future Past has a July 14, 2014 release date starring Jennifer Lawrence, James McAvoy, Michael Fassbender, Nicholas Hoult, Anna Paquin, Ellen Page, ShawnAshmore, with Hugh Jackman reprising as Wolverine, and returning cast members Patrick Stewart and Ian McKellan.